Equal density pellets or micro pellets

ABSTRACT

The invention relates masterbatches comprising pellets or micro pellets of one or more Single Pigment Concentrates (SPCs) and of one or more Additive Concentrates with at least two different chemical compositions, or of two or more Single Pigment Concentrates (SPCs) with at least two different chemical compositions, or of two or more Additive Concentrates with at least two different chemical compositions, characterised in that the pellets or micro pellets with different chemical compositions are of substantially equal density, size, shape and/or electrostatic properties. The invention further relates to a process for preparing said pellets or micro pellets in that a Single Pigment Concentrate (SPC) or Additive Concentrate with a chemical composition of specific weight is taken as reference and that the specific weight of all other SPCs or Additive Concentrates is adjusted to the specific weight of the reference by adapting the concentration of pigment (in the SPC) or additive (in the Additive concentrate) or by adding a filler or a blowing agent to the SPCs or Additive Concentrates.

BACKGROUND OF THE INVENTION

For coloring polymers, the plastic manufacturers prefer to purchaseready to use products from color manufacturers instead of working withthe basic colorants (pigments and dyes) which require a comprehensiveformulation and color matching expertise in order to achieve therequested color and the specific properties of the polymers.

The most common product forms sold by the color manufacturers arepre-colored resins or color concentrates. Color concentrates contain ahigh concentration of pigments or dyes in a carrier system. Such colorconcentrates are mixed by the plastic manufacturer with uncoloredpolymer and are then manufactured into semifinished products or finalproducts. The color concentrates are commonly used in pelletized form(also known as masterbatches) or liquid form (also known as liquidcolor).

The manufacturers of pre-colored resins use virgin resin and addcolorants and functional additives. The final product is a pellet whichis ready for processing. Compared to other methods of coloring resin,the use of pre-colored resin is a rather expensive manufacturingpractice. Pre-colored resin is much more expensive than uncolored resinplus a color concentrate.

The manufacturers of color concentrates frequently have to produce smallquantities of masterbatches (usually 10 to 50 kg) within short leadtimes due to the fact, that the plastic manufacturers want to keep onlyminimal stock of color concentrates in case a color becomes suddenlyobsolete.

The color concentrates, either in liquid form or in the pellet form(masterbatch) have to be mixed with the uncolored resin in a particularlet-down ratio in order to achieve the desired color. The mixing can bedone either by manual mixing, or, more commonly, by a batch-blendprocess using automated dosing equipment.

Liquid colors are normally pumped directly into the feed throat of theprocessing machine (e.g. an injection molding machine, a blow moldingmachine, a melt spinning system or the like) by using a smallperistaltic pump. A problem related with liquid color concentrates is,that the liquid carrier can have a negative impact on the physicalproperties of the polymer. Further disadvantage of liquid colorscompared to masterbatches are a more difficult handling, the cleaning ofthe machine between color changes, and the processing of the liquidcolor. However, the coloring costs with liquid colors are lower comparedto conventional masterbatches.

For most plastic manufacturers, the use of masterbatches is thepreferred method for coloring of plastics. Ease of handling and lowcosts compared to pre-colored resins are the main advantages for theseproducts. Unlike liquid colors, the compatibility of masterbatches withthe resin is excellent, since the carrier material of the masterbatch isin most cases identical with the resin.

An example of such automated dosing equipment for masterbatches is thevolumetric feeding unit as represented by FIG. 1. The feeding unitcomprises a resin feeder next to a masterbatch feeder, a mixer in amixing area, a flap between the mixing unit and the hopper and a hoppermounted on an extruder or injection molder. The resin feeder, themasterbatch feeder, the mixer and the flap are controlled by a controlunit, comprising a detector at the passage way from the hopper to theextruder or injection molder.

Masterbatches are commonly supplied in pellet or in micro-pellet form.There are few ways to produce a masterbatch. The first and most commonway used by the masterbatch manufacturers is a so called one stepprocess. During this process, pigments (or dyes), functional additivesand the polymer carrier are mixed, the mixture is then processed througha dispersion unit, e.g. a co-rotating twin screw extruder.

The color concentrates (masterbatches) can also be obtained in a socalled two step process, wherein in a first step, the masterbatchmanufacturers produce a Single Pigment Concentrate (SPC). SPC is amasterbatch preparation containing only one pigment or dye (generally invery high concentration) fully dispersed in a resin carrier optionallycomprising further additives. This first process step is very similar tothe one step process.

In a second step, different SPCs are mixed together in order to achievethe required color specifications of the customer and to get the tailormade masterbatch. To reduce the pigment concentration, the SPCs aremixed together with some carrier resin. Since SPCs are already fullydispersed, only a mixing process is necessary. This can be performed forexample with a single screw or twin screw extruder.

Compared to the one step process, the two step process leads to a muchhigher flexibility in the production of tailor made masterbatches and isalso more cost-effective for the production of small production batches(low cleaning costs of the machines, higher output rate compared to theone step process). This is increasingly important since the colorlifetime in the plastics business is becoming shorter and the averagelot size is becoming smaller.

The main disadvantage of this process is that it requires a secondextrusion which raises the production cost of the resulting tailor-mademasterbatches and which can affect the mechanical properties of thecarrier polymer and therefore also the mechanical properties of thefinal product.

A possibility to avoid the second extrusion is to separately add eachSPC to the resin during processing. This requires a dosing equipment foreach SPC. The dosing units are mounted directly onto the feed throat ofthe processing equipment (e.g. an injection molding machine, a blowmolding machine, a melt spinning system or the like). This system, aso-called multi dosing system, is not commonly used because it is verysophisticated and expensive.

The direct feeding of pre-mixed SPCs in a single dosing system in orderto avoid the second extrusion, leads to a separation or de-mixing of thedifferent components due to the difference in bulk density, thedifference in electrostatic properties of the different components anddue to the difference in form and size of the pellets.

The separation or de-mixing can take place during the followingprocessing steps:

-   -   loading of the pre-mixed SPCs in transport or storage containers    -   transport of the pre-mixed SPCs in transport containers    -   pneumatic conveying from the storage containers into the dosing        unit    -   feeding of the injection molding or extrusion machine under the        influence of the equipment's' vibration.

The separation leads to inconsistent and inhomogeneous color of thefinal products.

The separation in a single dosing system can be avoided by using anautomated dosing equipment, i.e. a volumetric or gravimetric feeder. Thedosing unit is mounted directly onto the feed throat of the processingequipment (e.g. an injection molding machine, a blow molding machine, amelt spinning system or the like). The resin is filled either manuallyinto a hopper attached to the dosing unit or pneumatically conveyed fromsilos or storage containers directly into the dosing unit (see FIG. 1).

Another approach to avoid separation of components is disclosed inJP62009915, wherein a plastic molding method is described which providesfor plastic pellets with different load or properties which do notseparate in the feed. JP62009915 proposes to use larger pellets if thespecific gravity (density) and/or antistatic properties of the materialare low; or to use smaller pellets if the specific gravity (density)and/or the antistatic properties are high. The process of JP62009915therefore compensates the different densities of the material, as afirst parameter, by adapting the size of the pellets and, additionally,takes into account the dielectricity of the material as a secondparameter.

SUMMARY OF THE INVENTION

The present invention provides a method for preventing the separation ofat least two different Single Pigment Concentrates (SPC) and/or AdditiveConcentrates in pellet or micro pellet form.

Pellets or micro pellets according to the invention are characterised inthat one or more Single Pigment Concentrates (SPCs) and of one or moreAdditive Concentrates with at least two different chemical compositions,

-   or of two or more Single Pigment Concentrates (SPCs) with at least    two different chemical compositions,-   or of two or more Additive Concentrates with at least two different    chemical compositions,-   with substantially equal density are provided.

The invention thereby enables the preparation of more cost effectivetailor-made masterbatches with SPC and/or Additive Concentrates byavoiding the multi-extrusion. The invention further provides a processwith higher flexibility and reactivity in the production of tailor mademasterbatches.

In a further aspect, the invention provides:

-   -   a method of coloring plastic by using a blend (or mixture) of        SPCs of at least two components.    -   a method of bringing properties to the plastic by using a blend        (or mixture) of Additive Concentrates of at least two        components.    -   a method of coloring and bringing properties to the plastic by        using a blend of SPCs and Additive Concentrates of at least two        components.

The Additive Concentrates are defined as preparations containing atleast one active ingredient dispersed in a resin carrier, wherein theactive ingredient is selected from the group consisting ofanti-blocking, anti-fogging, anti-microbial, antioxidant, anti-slipping,anti-static or cleaning agents, compatibilizers, conductive agents,corrosion inhibitors, de-nesting agents, drying agents, fillers, flameretardants, foaming agents, infrared agents, laser marker agents,lubricants, matting agents, nucleating agents, opacifiers, opticalbrightener, phosphorescent agents, photo-degradable agents, processingaids and/or UV stabilisers.

The Single Pigment Concentrates (SPCs) are defined as preparationscontaining only one pigment or dye dispersed in a carrier resinoptionally comprising additives (see the list above). A SPC contains 20to 80% by weight of a pigment or a dye and 80 to 20% by weight of acarrier polymer. Pigments are inorganic or organic pigments.

The carrier polymer is a thermoplastic polymer or a blend ofthermoplastic polymers selected from polyolefins, polyesters,polyamides, polyacrylates, polycarbonates, polyurethanes, polystyrenesand copolymers thereof. It is required, that the carrier polymer for themasterbatch is compatible with the virgin polymer used for the finalproduct.

The SPCs and Additive Concentrates are provided in pellet or in micropellet form. The micro pellet form is preferred for an improved coloruniformity of the final product due to the smaller size and betterstatistical distribution of the micro pellets. The size of the pelletsis from larger than 2.0 mm to 4.0 mm; the size of the micro pellets isfrom about 0.5 mm to 2.0 mm.

This technology can be easily introduced in a variety of applicationsfor example in injection molding, blow molding, extrusion or spindyeing. The color consistency is insured from the beginning to the finalproduct since the mixture of the components stays homogeneous over thetime.

Preferred industrial applications for the masterbatches according to theinvention are blown film, blow molding, calendering, cast film,injection molding, pipe extrusion, profile extrusion, sheet extrusion,spin dyeing and stretch blow molding.

The main characteristics of the components (micro pellets or pellets)according to the invention are:

-   -   controlled density (specific weight) of the components (micro        pellets or pellets)    -   controlled size and shape of the components (micro pellets or        pellets)    -   controlled electrostatic properties of the components (micro        pellets or pellets)

Masterbatches according to the invention consist of micro pellets orpellets of different chemical composition but with substantially equaldensity.

The density of the pellets or micro pellets is from 0.5 to 1.5 g/cm³ andpreferably from 0.6 to 1.1 g/cm³.

Preferred masterbatches according to the invention consist of micropellets or pellets of different chemical composition but withsubstantially equal density and substantially equal size and shape.

Most preferred masterbatches according to the invention consist of micropellets or pellets of different chemical composition but withsubstantially equal density, substantially equal size and shape andsubstantially equal electrostatic properties.

Micro pellets or pellets of different chemical composition but withsubstantially equal density according to the invention are obtained byadjusting the pigment content, by adjusting the filler content and/or byadding a blowing agent to produce a hollow pellet.

Micro pellets or pellets of different chemical composition but withsubstantially equal density and substantially equal size and shape areobtained by adjusting the pigment content, adjusting the filler contentand/or adding a blowing agent to produce a hollow pellet and subjectingthe blend to the same production and shaping process.

To prevent the separation of the mixture due to the electrostatic chargeof the components, an antistatic additive (for example stereates orlauryl amides) is added in the blend to obtain the most preferredmicro-pellets or pellets of different chemical composition but withsubstantially equal density, substantially equal size and shape andsubstantially equal electrostatic properties.

The invention therefore enables the production of SPCs and AdditiveConcentrates of different chemical composition with the same specificweight (density) of the pellets or micro-pellets.

The adjustment of the parameters of the different SPCs and AdditiveConcentrates can be achieved as follows:

1) Take the SPC or Additive Concentrate with the composition of lowerspecific weight as reference and reduce the specific weight of all otherSPCs and Additive Concentrates to the specific weight of the referenceby:

-   -   reducing the concentration of pigment (respectively additive) of        the SPCs or Additive Concentrates    -   or by adding a blowing agent in order to form “hollow” pellets        or micro pellets.

2) Take the SPC or Additive Concentrate with the composition of higherspecific weight as reference and increase the specific weight of allother SPCs and Additive Concentrates to the specific weight of thereference by

-   -   adding a filler.

The filler can include every material or composition having a higherdensity than the reference like for example oxides, carbonates, sulfatesand silicates.

3) Take one of the SPCs or Additive Concentrates as a reference andincrease the specific weight of the SPCs or Additive Concentrates withlower specific weight to the specific weight of the reference and reducethe specific weight of the SPCs or Additive Concentrates with higherspecific weight to the specific weight of the reference as describedabove.

In the following, two possible procedures for obtaining equal densitypellets or micropellets are described in detail. Although the procedureis described for SPC's, it is mutually applicable to AdditiveConcentrates as well as to mixtures of SPC's and Additive Concentrates.

A) A standard SPC with a particular concentration in a selected polymeris identified as a reference. Then the SPC's to be adjusted at equaldensity are extruded in the same shape and size in the same selectedpolymer.

The relative density compared to the reference is determined. For thoseSPC's with a higher density, the pigment and/or filler load isdecreased. For those SPC's with a lower density, the pigment and/orfiller load is increased.

In an itterative process, the SPC's are again extruded in the same shapeand size in the same selected polymer and the relative density is againcompared to the reference. The itterative process is terminated when thedensity of the adjusted SPC's is within a defined density range close tothe reference.

B) A standard SPC at a particular concentration in a selected polymer isidentified as a reference. Then the SPC's to be adjusted at equaldensity are extruded in the same shape and size in the same selectedpolymer.

The relative density compared to the reference is determined. For thoseSPC's with a higher density, the amount of blowing agent is increased.For those SPC's with a lower density, the amount of blowing agent isdecreased.

In an itterative process, the SPC's are again extruded in the same shapeand size in the same selected polymer and the relative density is againcompared to the reference. The itterative process is terminated when thedensity of the adjusted SPC's is within a defined density range close tothe reference.

Preferred fillers are calcium salts, barium salts or silicates. Inparticular preferred are carbonates, sulphates and silicate hydrates, aswell as so called clays and nano-clays. Most preferred fillers arecalcium carbonate and barium sulphate.

In principal, fillers as used in the present invention are defined to becompounds with a density above 1 g/cm³ according to ISO 787-10.

Preferred blowing agents are chemical blowing agents, in particularendothermic or exothermic blowing agents, for example such as areavailable in the Hydrocerol® range of Clariant.

Antistatic agents are added, when necessary, to the SPCs and AdditiveConcentrates to prevent the de-mixing of the mixture, respectively theblend, due to electrostatic charge of the SPCs or Additive Concentrates.

All the tests performed in the examples show that the mixture ofdifferent SPCs and or Additive Concentrates with equal density accordingto the invention, stay homogeneously mixed, e.g. when vibrated with aback and forth shaker, compared to a mixture of SPCs with non-equaldensity.

EXAMPLES

Equal Density Adjustment of SPCs:

As a standard organic SPC, a C.I. Pigment Red 214 (commerciallyavailable form Clariant as PV Fast Red BNP) at a concentration of 40% inpolypropylene has been identified as a reference with a bulk density of0.62 g/cm³ (see F below).

Then the SPCs to be adjusted at equal density have been extruded inpolypropylene and pelletized in cylindrical shape at a size of 3 mmlength and 2 mm diameter.

250 g of each of the SPC pellets have been put in a measuring glasscontaining 500 ml of water. The pellets were kept under water by puttinga screen above. The difference in density compared to the reference hasbeen determined by comparing the difference in waterlevel in themeasuring glass.

For those SPC's where the waterlevel is lower than the reference(=higher density), the pigment and/or filler load has been decreased.E.g. for a SPC of C.I. Pigment White 6 containing 70% of TiO₂, the TiO₂load has been reduced to 28% in several itterative steps (see A below).

The itterative process was terminated when the density of the adjustedSPC's were within a density range of +/−0.02 g/cm³ to the reference.

For those SPC's where the waterlevel is higher than the reference(=lower density), the pigment and/or filler load has been increased.E.g. for a pure polypropylene, 30% of CaCO₃ were added as a filler inseveral itterative steps.

The itterative process was terminated when the density of the adjustedPP was within a density range of +/−0.02 g/cm³ to the reference.

The following SPCs have been prepared as described:

-   A) White C.I. Pigment White 6: 28% of TiO₂ has been mixed with 72%    of polypropylene and the mixture has been dispersed with a twin    screw extruder.-   B) White 2 C.I. Pigment White 6: 70% of TiO₂ has been mixed with 30%    of polypropylene and the mixture has been dispersed with a twin    screw extruder.-   C) Yellow C.I. Pigment Yellow 34: 27% of Chrome Yellow has been    mixed with 63% of polypropylene and the mixture has been dispersed    with a twin screw extruder-   D) Yellow C.I. Pigment Yellow 119: 25% of Zinc/Ferric oxide has been    mixed with 75% of polypropylene and the mixture has been dispersed    with a twin screw extruder-   E) Black C.I. Pigment Black 7: 35% of Carbon black has been mixed    with 65% of polypropylene and the mixture has been dispersed with a    twin screw extruder.    -   The bulk density of these SPCs has then been adjusted to        0.62+/−0.02 g/cm³ according to ISO 697 by adjusting the        concentration of the pigment dispersed in the polymer carrier.        And-   F) Red C.I. Pigment Red 214: 40% of PV Fast Red BNP (commercially    available form Clariant) has been mixed with 60% of polypropylene    and the mixture has been dispersed with a twin screw extruder    -   The bulk density of this SPCs has not been adjusted, as it was        used as a reference for adjusting A and C-E above as well as G        below.

The following Additive Concentrate has been prepared as described:

-   G) Anti-oxidant Irganox® B501W (Trademark of Ciba Specialities    Inc.): 15% of Irganox B501W has been mixed with 30% of calcium    carbonate and 55% of polypropylene and the mixture has been    dispersed with a twin screw extruder.

The bulk density of this Additive Concentrate Blend has been adjusted to0.62+/−0.02 g/cm³ according to ISO 697 by adding a filler (calciumcarbonate). Component (SPC or Bulk Density Additive Concentrate) (g/cm³)A White P.W. 6 0.60-0.62 B White 2 P.W. 6 1.04-1.06 C Yellow PY 340.60-0.62 D Yellow PY 119 0.61-0.63 E Black P.Bk. 7 0.60-0.62 F Red P.R.214 0.62-0.64 G Irganox ® B501W 0.62-0.64

Examples 1-4

The following batches have been prepared: Batch 1 9.98% Irganox ® B501W78.63% White P.W. 6 4.27% Yellow P.Y. 34 6.30% Yellow P.Y. 119 0.82%Black P.Bk. 7 Total batch size: 50 g + 0.025 g Nopcostat ® HS(Antistatic) (Trademark of Cognis) Batch 2 6.63% Irganox ® B501W 31.84%White P.W. 6 56.52% Yellow P.Y. 34 2.95% Red P.R. 242 2.06% Black P.Bk.7 Total batch size: 50 g + 0.025 g Nopcostat ® HS (Antistatic)(Trademark of Cognis) Batch 3 9.98% Irganox ® B501W 78.63% White P.W. 64.27% Yellow P.Y. 34 6.30% Yellow P.Y. 119 0.82% Black P.Bk. 7 Totalbatch size: 50 g Batch 4 6.63% Irganox ® B501W 31.84% White P.W. 656.52% Yellow P.Y. 34 2.95% Red P.R. 242 2.06% Black P.Bk. 7 Total batchsize: 50 g

The following tests have been carried out:

The batches 1 to 4 have been agitated with a back and forth shaker fromInfors AG at the speed of 400 rpm for 24 hours.

Batches 1 and 2 (with antistatic agent) stay substantially homogeneouswhereas the batches 3 and 4 (without antistatic agent) show asignificantly higher de-mixing tendency due to electrostatic charging.

Comparative Examples 5-8

The following 3 batches have been prepared by filling two separatelayers in a bottle: Batch 5 Upper layer: 50.0% White 2 P.W. 6 Bottomlayer: 50.0% Black P.Bk. 7 Total batch size: 50 g Batch 6 Upper layer:50.0% Black P.Bk. 7 Bottom layer: 50.0% White 2 P.W. 6 Total batch size:50 g Batch 7 Upper layer: 50.0% White P.W. 6 Bottom layer: 50.0% BlackP.Bk. 7 Total batch size: 50 g

The following batch has been prepared by filling a random mixture in abottle: Batch 8 50.0% White P.W. 6 50.0% Black P.Bk. 7 Total batch size:50 g

The following tests have been carried out:

The Batches 5 to 8 have been agitated with a back and forth shaker fromInfors AG at the speed of 400 rpm for 24 hours.

The two layers of Batch 5 were completely mixed due to the difference ofbulk densities, whereas in Batch 6 only a few black granules arrived inthe white layer. (In Batch 6 the higher density of the white componentprevents the pellets from moving upward whereas the lower density of theblack component prevents the pellets from moving downward.)

The two layers of Batch 7 stayed substantially separate due to the equalbulk density. (Only a few black and white granules arrived in theopposite layer.)

In the random mixture of Batch 8 no de-mixing could be observed due tothe equal bulk density.

1. Pellets or micro pellets of one or more single pigment concentratesand of one or more additive concentrates, wherein the one or more singlepigment concentrates and the one or more additive concentrates have atleast two different chemical compositions, or two or more single pigmentconcentrates with at least two different chemical compositions, or twoor more additive concentrates with at least two different chemicalcompositions, wherein the pellets or micro pellets are of substantiallyequal density.
 2. Pellets or micro pellets according to claim 1, whereinthe pellets or micro pellets are of substantially equal size.
 3. Pelletsor micro pellets according to claim 1, wherein the pellets or micropellets are of substantially equal shape.
 4. Pellets or micro pelletsaccording to claim 1, wherein the pellets or micro pellets havesubstantially equal electrostatic properties.
 5. Pellets or micropellets according to claim 1, wherein the particle size of the pelletsis from larger than 2.0 mm to 4.0 mm.
 6. Pellets or micro pelletsaccording to claim 1, wherein the density of the pellets or micropellets is from 0.5 to 1.5 g/cm³.
 7. A masterbatch comprising pellets ormicro pellets according to claim
 1. 8. A process for the preparation ofpellets or micro pellets according to claim 1, comprising the step offorming a reference from the single pigment concentrate or additiveconcentrate with the chemical composition of lower specific weight andreducing the specific weight of the one or more single pigmentconcentrates and/or one or more additive concentrates to the specificweight of the reference by reducing the pigment concentration of the oneor more single pigment concentrates and/or reducing the additiveconcentration of the one or more additive concentrates.
 9. A for thepreparation of pellets or micro pellets according to claim 1, comprisingthe steps of forming a reference from the single pigment concentrate oradditive concentrate with the chemical composition of lower specificweight and that and reducing the specific weight of the one or moresingle pigment concentrates and/or the one or more additive concentratesto the specific weight of the reference by adding a blowing agent to theone or more single pigment concentrates and/or additive concentrates.10. A Process for the preparation of pellets or micro pellets accordingto claim 1, comprising the step of forming a reference from the singlepigment concentrate or additive concentrate with the chemicalcomposition of higher specific weight and increasing the specific weightof the one or more single pigment concentrates and/or one or moreadditive concentrates to the specific weight of the reference by addinga filler to the one or more single pigment concentrates and/or one ormore additive concentrates.
 11. A process for making a masterbatchcomprising the step of adding pellets or micro pellets according toclaim 1 to reaction mixture during the manufacture of the masterbatch.12. A process for coloring and/or imparting additive properties on aplastic comprising the step of adding pellets or micro pellets accordingto claim 1 to the reaction mixture during the formation of the plastic.13. The process according to claim 12, wherein the plastic is in theform of a fiber.
 14. A plastic article made with at least onemasterbatch according to claim
 7. 15. Use according to claim 14 of themasterbatches according to claim 7 for bringing color and additiveproperties into fibres.
 16. Pellets or micro pellets according to claim1, wherein the particle size of the micro pellets is from 0.5 to 2.0 mm.17. Pellets or micro pellets according to claim 1, wherein the particlesize of the pellets is from larger than 2.0 mm.
 18. Pellets or micropellets according to claim 1, wherein the particle size of the pelletsis from larger than 4.0 mm.
 19. Pellets or micro pellets according toclaim 1, wherein the density of the pellets or micro pellets is from 0.6to 1.1 g/cm³.
 20. A plastic made in accordance with the process of claim12.